I. Field of the Invention
The present invention relates generally to antennas and, more particularly, to a microwave antenna system.
II. Description of Related Art
A phased array antenna is oftentimes used to electronically scan a radar or microwave beam echo. Such microwave antenna systems are used in many different applications, including automotive applications.
These previously known phased array microwave antenna systems typically include a number of antenna elements that are linearly arranged from one end and to the other end and in which the antenna elements are equidistantly spaced from each other. In order to control the direction of the antenna scan, phase shifters are employed to modify the phase of the incoming received signals so that the signals combine in the desired direction of the antenna system.
One approach for controlling the phase shift in the antenna array elements is to provide a phase shifter for every single element in the array. Such a design gives near ideal performance to control the direction of the radar beam.
A disadvantage, however, of providing a phase shifter for every element in a phased array antenna system is that the phase shifters are relatively expensive and increase the complexity of the radar transceiver module. Consequently, providing a phase shifter for every element in the array dramatically increases not only the cost, but also the size, of the transceiver module for the radar system. In many types of systems, for example automotive systems, it is difficult to justify the cost of individual phase shifters for every array element.
In one prior design, a single phase shifter was connected to each pair of adjacent antenna elements thus effectively reducing the number of required phase shifters for the antenna system by one half. This approach, however, disadvantageously resulted in the generation of grating lobes for the received microwave signal. Such grating lobes cause targets outside the field of view to appear as if they are actually inside the field of view and are known as ghost targets. These ghost targets cannot be distinguished from the real target and, as a result, the scannable area of the phased array is reduced.